There has been considerable interest in recent years in nonaqueous secondary cells because of the possibilities afforded of obtaining cells useful for small electronic applications, e.g., calculators, circuit boards, and watches, which overcome drawbacks, e.g., self-discharge and low voltage, of the presently used nickel-cadmium cells. Many materials have been considered as candidates for the electrode materials in such cells. Classes of materials that undergo topochemical reactions are potentially useful as the active positive electrode materials in secondary cells and thus have received particular attention. Broadly speaking, topochemical reactions involve a host lattice into which a guest species is inserted with the product maintaining the essential structural features of the host. When the structural changes are minimal, this process is called intercalation and is likely to be readily reversible. This reversibility of the intercalation reaction may form the basis for a secondary cell if the reaction is of the oxidation-reduction type.
Topochemical reactions of alkali metals and several types of transition metal compounds appear to be especially promising candidates for use in secondary cells. The use of layered transition metal selenides and sulfides as the active positive electrode materials in such cells has received must attention. However, transition metal oxides, other factors equal, are more desirable electrode materials than are sulfides and selenides because they may afford higher energy densities per unit weight and/or per unit volume. Additionally, oxides are less noxious than are sulfides and selenides or decomposition.
Several transition metal oxides have been studied for use as electrode materials. For example, V.sub.2 O.sub.5 was used in a primary cell by Dey et al., U.S. Pat. No. 3,655,585; MoO.sub.3 was studied by Dampier, Journal of the Electrochemical Society 121, 656 (1974); and MnO.sub.2 was studied by Ikeda et al., Manganese Dioxide Symposium 1, 384 (1975). The use of V.sub.2 O.sub.5 in a secondary cell was reported by Walk and Gore, Electrochemical Society Meeting, Paper No. 27, Toronto, May 11-16 (1975). However, secondary cells using V.sub.2 O.sub.5 as the positive electrode material suffer from several drawbacks, e.g., the low electronic conductivity of V.sub.2 O.sub.5 and its irreversible reduction at moderate potentials. Additionally, electrolyte oxidation occurs during charging of such cells.